If I want to see only one country's tanks, I have to click all 10 other countries to unselect them - and then re-click all 10 when I'm done. It should work like tank tier - if I want to see only one tier, I click that tier and that does it. When I'm done, one click and all tiers are shown.

um ok there might be something up with your game cause without mods all I have to do is input like 2 clicks and I can hide all but 1 country at a time